Johnson HD-20 Won’t start

[jsonova99]

I’m trying to get this started for the first time, before I commit to the full cosmetic restoration. Here is what I have:

compression : ~72 psi per cylinder
spark: yes
fuel: the carb is filling as I can see the float pin come up. I can prime it and get fuel slightly leaking out of the low speed carb and I can here is sucking air when I turn it over.
Settings: high speed 3/4 turn from seated, low speed 5/8 turn from seated
Fuel ratio: ~16:1 (on the rich side)

In theory it should start I think. I get nothing unless I take a syringe of fuel and it shoot it right into the low speed carb. If I turn it over I can here it catch quickly, but only fire each cylinder maybe once, until that shot of gas is gone I assume. When I do squirt the gas in though, I notice that it leaks out around the sides where the low speed carb goes into the engine. My guess is that this is a clue. Otherwise I’m stumped. Is the low speed carb threaded in? Should I remove it and seal it? Like I said, I can hear the low speed carb sucking air, but it’s like it’s not sucking any fuel in.

One other note, I tried starting it yesterday and concluded had no spark, but, while pulling the plugs to ground them to the chassis for a spark check, I noticed that they had no gasoline smell at all, which probably confirms my suspicion that fuel is not being pulled in. The fact that priming causes fuel to leak out of the low speed carb tells me that fuel is flowing, no blockages. I pulled the stator apart and cleaned up the points and confirmed spark this morning before putting it all back together.

On a sidenote, my starter rope is coming apart (cloth covered steel braided wire), any ideas on a replacement?

Thanks in advance, I feel like I’m getting close on this one.

[garry-in-michigan]

The low speed venturi is a press fit. Multiple primes should have fuel dripping out the front. If the motor stilted forward, little will get into the engine. When on a boat, the weight at the transom tilts it toward the back aiding the prime. Replace the starter rope with quarter inch woven nylon rope. Fuze the ends with heat to keep it from un-raveling.

[steveh]

My first thought is that the low speed needle may not be open enough. About 5/8ths of a turn from gently closed. The high speed needle should be open about 3/4 of a turn.

On my HD-25, it takes a little while to get it started when it is cold. I pump the primer about 6 times, give the cord one yank. Then another press on the primer and another yank. It will usually pop, and then I hit the primer button two or three times. It usually goes after that.

[aquasonic]

These are finicky little motors. Everything needs to be ‘just right’ for a good runner. The fact that the sparkplugs are dry, leads me to think that there may be carburetor problem.

Have you completely taken the carb apart, soaked it in solvent, blown out the passages with compressed air, cleaned the fuel lines, refinished or replaced the float, replaced the leather primer washers, polished the float needle, cleaned the float needle seat, polished the high speed needle, checked/replaced the low speed packing, and cleaned/inspected the primer check valve?

Your motor is from 1941 or 1942, and if it hasn’t been done yet, a ‘whole nine yards’ carburetor cleaning/rebuild is long overdue.

[jsonova99]

Replacing the leather primer washers I haven’t done yet but I am getting ready to send my money out for a pair. I figured I’d try ahead of time while waiting. Explain the low speed packing to me. Otherwise I’ve done everything mentioned.

I agree though, I think it’s a fuel delivery problem, too. Everything else checks out. I’m trying to think what passages I could have missed on it with cleaner and compressed air. Like I said the carb does appear to fill up (reconditioned float with fuel proof dope) and doesn’t flood so everything bringing fuel to the float chamber should be fine, and float needle seat should be good since it doesn’t overflow. Definitely something to the combustion chamber being dry until I forced fuel in.

[aquasonic]

I can tell you from experience that the high and low speed systems are very closely linked in this smallest of rotary valve motors. I have had a few frustrating times with trying to get mine started, only to find out that the low speed needle had backed out way past where it should have been. That caused a too rich wet plug problem though.

It sounds as if your float and float needle are working correctly. When the gas is opened, the float pin goes up, and no flooding, so that’s good. I’m not sure about the specifics of the fuel leaking around the venturi. When you prime the carb, fuel should come out of the open part but not from anywhere else.

There are two tiny packing washers around the low speed needle that sit on a concave seat. When the packing nut gets tightened, the washers get compressed around the needle and seals off air from getting in past the needle. They perform an important job. Do you have the packing nut tightened properly?

There is a procedure for removing the venturi. I have never had to do this, but I do recall reading that it is pressed in with lead shims. That would be the last thing that I would try, but who knows.

Bear in mind that the high and low speed systems take two different paths through the carburetor, and there could still be a blockage in the high speed system while the low speed and primer seem to work fine.

[steveh]

It has been awhile since I’ve had mine apart, but there is also a very small tube visible when you take the carb/exhaust plate off the motor. It can plug up and not allow gas through. In that case, I could start and run mine slowly, but not at high speed.

[jsonova99]

Does the primer only prime the low speed? The leakage I see around the low speed venturi is only if I shoot fuel into it with a syringe so I’m not too concerned about it. When I push the primer a few times, I see a little fuel leak out of the hole which sounds common. The low speed packing washers have my attention, I don’t think there is anything in there currently. What could I use as a replacement for them?

If this were the problem, would it explain not getting any fuel into the combustion chamber? I couldn’t believe that after the first round of trying to start it the plugs were totally dry until I forced fuel in.

[kevinf]

Is the fuel leak when you prime it from the low speed venturi ? If the low speed circuit is clean you should see some fuel spray there. For a first run I usually end up spraying a syringe of gas oil mix in the low speed venturi as you’ve done. Normally that’s enough to get a few seconds of run time while I fool with the needle valve. The motor should run on the low speed alone and once I have that working I open the needle on the high speed.
I’m sure others have more experience than I but that sequence has always worked for me and lets me deal with one issue at a time 🙂

Kev

[burnt-clutch]

quote SteveH:

It has been awhile since I’ve had mine apart, but there is also a very small tube visible when you take the carb/exhaust plate off the motor. It can plug up and not allow gas through. In that case, I could start and run mine slowly, but not at high speed.

Sorry if I’m hijacking this thread, but would this tube be on a HD 25 as well? I’ve had my carb and intake apart but I haven’t noticed this. My HD 25 runs the same way that you describe.
-Karl

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